Synthesis and chemistry of some pyridazine nucleosides related to certain 5‐substituted pyrimidine nucleosides

Condensation of 3,4‐dichloro‐6‐[(trimethylsilyl)oxy] pyridazine (3) with 1‐O‐acetyl‐2,3,5‐tri‐O‐benzoyl‐β‐D‐ribofuranose (4), by the stannic chloride catalyzed procedure, has furnished 3,4‐dichloro‐1‐(2,3,5‐tri‐O‐benzoyl‐β‐D‐ribofuranosyl) pyridazin‐6‐one (5). Nucleophilic displacement of the chloro groups and removal of the benzoyl blocking groups from 5 has furnished 3‐chloro‐4‐methoxy‐, 3,4‐dimethoxy‐, 4‐amino‐3‐chloro‐, 3‐chloro‐4‐methylamino‐, 3‐chloro‐4‐hydroxy‐, and 4‐hydroxy‐3‐methoxy‐1‐β‐D‐ribofuranosylpyridazin‐6‐one. An unusual reaction of 5 with dimethylamine is reported. Condensation of 4,5‐dichloro‐3‐nitro‐6‐[(trimethylsilyl)oxy]pyridazine with 4 yielded 4,5‐dichloro‐3‐nitro‐1‐(2,3,5‐tri‐O‐benzoyl‐β‐D‐ribofuranosyl)pyridazin‐6‐one (24). Nucleophilic displacement of the aromatic nitro groups from 24 is discussed. Condensation of 3 with 3,5‐di‐O‐p‐toluoyl 2‐deoxy‐D‐erythro‐pentofuranosyl chloride (28) afforded an α, β mixture of 2‐deoxy nucleosides. The synthesis of certain 3‐substituted pyridazine 2′‐deoxy necleosides are reported.